Today, many computing devices have significant computational power and capabilities, yet are small enough and light enough that they can be easily carried. However, having such small sizes typically means that these devices have correspondingly small and limited interaction mechanisms, such as in the form of diminutive screens, buttons, and/or jog wheels. This diminishes the usability and functionality of such devices, because simply making buttons and screens larger results in losing the benefit of small device size.
One option is to opportunistically appropriate a surface area for interactive purposes. For example, one technique allows a small mobile device to use a table on which it rests as a gestural finger input canvas. However, a table is not always available for use, and in a mobile context, it is highly unlikely that users will be willing to carry such a surface with them; (indeed, at this point a user would probably prefer to simply have a larger device).